Blood concentrations and clinical findings in 25 cases of overdose involving chlordiazepoxide (CDZ) alone ("pure") were compared with those in 23 cases of overdose involving ethanol in addition to CDZ ("mixed"). Both groups consisted predominantly of men who were chronic alcoholics. The mean blood CDZ concentrations did not show statistically significant difference between the two groups ("pure," 5 mg/L; "mixed," 6 mg/L). Following "pure" ingestion, patients were usually alert, and the level of consciousness showed no statistically significant correlation with the blood CDZ concentration. In contrast, after "mixed" ingestion patients were usually lethargic, and the level of consciousness correlated significantly with the blood CDZ concentration (P less than 0.05) but not with the blood ethanol concentration. In neither group was coma noted. For both groups the most common physical findings were tachycardia and dysarthria. Nystagmus was much more common following "mixed" ingestion while seizures, hyperreflexia, and hypertension were more frequent after CDZ overdose alone. Most patients were seen only in the emergency room and were discharged. The implications of these findings are discussed.